Developments in semiconductor devices are accompanied by increasingly higher degrees of element integration, resulting in increased miniaturization of each element and a reduction in operating voltage. For example, in the field of MONOS (metal oxide nitride oxide semiconductor)-type non-volatile semiconductor devices which include a blocking film that separates a charge retaining layer and a gate electrode, the miniaturization of elements has led to demands for higher permittivity in blocking films. Similarly, in the field of FG (floating gate)-type non-volatile semiconductor devices, the miniaturization of elements has led to demands for higher permittivity in insulating films between a floating electrode and a gate electrode. In addition, in the field of advanced DRAM (dynamic random access memory) devices, in order to secure capacitance of capacitors making up miniaturized memory cells, dielectric film are required which have high permittivity and are capable of accommodating a thinner film thickness without causing an increase in leakage current. Furthermore, in the field of advanced CMOS device development, techniques for reducing gate leakage current by increasing the physical thickness of a gate insulating film using high permittivity material are being considered. Moreover, it is required that high dielectric films are heat-resistant with respect to a 1000° C.-annealing treatment performed during the manufacturing process of the semiconductor devices described above. Furthermore, it is required that the surfaces of high dielectric films have superior flatness for the purpose of suppressing variations in the operating voltages of the semiconductor devices.
As means for increasing the relative permittivity of a dielectric film, the use of HfO2, ZrO2, and Al2O3 as dielectric films having a higher relative permittivity than conventional SiO2 film, SiN film, or SiON film combining the two, is being considered. In addition, more recently, research is being performed on dielectric films in which a metallic element is doped on a laminated (stacked) structure made of HfO2, ZrO2, or Al2O3 or on HfO2 or ZrO2 for the purpose of suppressing leakage current associated with thinner dielectric films.
For example, Non-Patent Documents 1 and 2 disclose dielectric films in which silicon (Si), yttrium (Y), lanthanum (La), or the like is doped as a metallic element on HfO2. According to Non-Patent Document 1 and 2, it is described that, by doping the metallic element described above on HfO2 and performing crystallization thereon, HfO2 having a tetragonal crystalline phase is formed and a high relative permittivity value of 28 is obtained.
Non-Patent Document 3 discloses a dielectric film in which TiN is laminated (stacked) on the surface of HfO2. According to Non-Patent Document 3, it is described that, when crystallization is performed in a state where TiN is laminated on HfO2, HfO2 having a cubic crystalline phase is formed and a high relative permittivity value of 50 is obtained.
Patent Document 1 discloses a dielectric film in which a metallic element such as yttrium (Y), magnesium (Mg), calcium (Ca), or lanthanum (La) and nitrogen are doped on HfO2. According to Patent Document 1, it is described that, by adding an element with a large atomic radius such as Y, Mg and Ca described above to monoclinic HfO2, the aggregated energy of the cubical crystals decreases and stabilizes, thereby altering the crystalline system of HfO2 from monoclinic crystal to tetragonal crystal and then to cubical crystal. As a result, a high dielectric film made of HfYO with a relative permittivity of 70 can be obtained. In addition, as oxygen in the monoclinic HfO2 is replaced with nitrogen, the crystalline system changes from monoclinic crystal to tetragonal crystal, to rhombohedral crystal, and then to cubical crystal as the amount of nitrogen increases.
Patent Document 2 discloses a technique for using, as a dielectric film material, a composition including HfO2 having a cubic crystalline phase and a second compound. According to Patent Document 2, it is described that a HfO2 cubical crystal containing 1 mol % to 50 mol % of Al2O3 as the second compound has a relative permittivity of 29.8, which is higher than pure HfO2.
Patent Document 3 discloses, as a dielectric film, a noncrystalline film in which noncrystalline aluminum oxide is contained in a crystalline dielectric film and which is formed of AlM(1-x)Oy (where M is a metal such as Hf and Zr capable of forming a crystalline dielectric body) having a composition expressed as 0.05 <×<0.3. According to Patent Document 3, it is described that a high relative permittivity ranging from 25 to 28 can be obtained with noncrystalline zircon aluminate.
Non-Patent Document 4 discloses a dielectric film material made of HfAlON. According to Non-Patent Document 4, it is described that HfAlON whose Hf/(Hf+Al) composition ranges from 20% to 80% and whose nitrogen composition is 30% or higher acquires a noncrystalline structure at an annealing temperature of 850° C. and has a relative permittivity ranging from 10 to 25.
Patent Documents
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-25995
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-161602
Patent Document 3: Japanese Patent Application Laid-Open No. 2004-214304
Non-Patent Documents
Non-Patent Document 1: Applied Physics Letters 86, 102906, 2005
Non-Patent Document 2: International Electron Devices Meeting Technical Digest, 2007, p. 53
Non-Patent Document 3: Symposium on VLSI Technology Digest of Technical Papers, 2008, p. 152
Non-Patent Document 4: Japanese Journal of Applied Physics Vol. 44, No. 4B, 2005, p. 2311